Traumatic events are quite common among the U.S. population (70%), and a small but significant number of trauma survivors will develop posttraumatic stress disorder (PTSD) in the aftermath of a trauma. PTSD is an anxiety disorder characterized by psychological reexperiencing of the traumatic event, avoidance of trauma reminders, and physiological hyperarousal. Recent theoretical advances regarding the development and maintenance of PTSD propose that trauma-induced changes in thoughts and beliefs about the self and the world may contribute to PTSD. Effective treatments have been developed for PTSD, yet little is known about the mechanisms at work in these treatments. Changes in trauma-related cognitions may be one pathway through which treatments are helpful at reducing PTSD. Further, even the best treatments for PTSD are not effective for all patients. Thus, it is of both theoretical and practical importance to understand the relationship between trauma-related cognitions and PTSD symptom severity, and how change in cognitions unfolds during treatment. Adult participants with PTSD will be recruited as part of a NIMH-funded randomized, controlled clinical trial comparing the effectiveness of prolonged exposure therapy (PE) and sertraline for chronic PTSD. The following specific aims are proposed: (1) To test the relationship between trauma-related cognitions and PTSD symptom severity in traumatized adults, and to compare overall change in trauma-related cognitions in the PE group to that of the sertraline group; (2) To examine the relationship between early, reliable change in trauma-related cognitions and PTSD symptom severity using established statistical methods (e.g. Jacobson & Truax, 1991; Devilly & Foa, 2001); and (3) To explore temporal patterns of change in cognitions and PTSD symptom severity in the PE group compared to the sertraline group. Negative trauma-related cognitions and PTSD symptom severity will be measured pretreatment, at each treatment session, posttreatment, and at 6-month follow-up. Should the data support a relationship between cognitive change and PTSD symptom severity, secondary analyses will be conducted to examine the demographic, trauma-specific, and treatment-related predictors of cognitive change, thus broadening the implications of the study. [unreadable] [unreadable] [unreadable]